1. Field of the Invention
This invention relates to heat transfer mechanisms and more particularly heat transfer mechanisms for removing the heat generated in an electronic circuit module assembly.
2. Related Art
The efficient extraction of heat from electronic circuit modules for very large scale integrated circuit (VLSI) packages has presented a significant limitation on the design and use of such electronic modules. The power consumed in the integrated circuits generates heat which must in turn be removed from the VLSI package. Lacking an efficient heat transfer mechanism, the speed, reliability and power capabilities of the electronic circuit modules are severely limited. As the density of circuits within VLSI chips has increased, the need for improved heat extraction has become even more acute since the more densely packed chips tend to have a higher need for heat dissipation per unit area.
One conventional means of heat extraction has been through the use of an encapsulated thermal conduction module of the type shown in FIG. 1. The thermal conduction module 10 of FIG. 1 provides cooling of the integrated circuit chips 12 contained therein. The chips 12 are mounted on one side of a substrate 14, generally made of ceramic, which has pins 16 extending from the other side thereof. As is conventional, the integrated circuit chips are arranged on the substrate in a row and column array. The pins 16 provide for the plugging of the module into a board (not shown) which may carry connecting circuitry, etc. A housing cap 18 is attached to the substrate 14 by means of a flange 20 which extends from the periphery of the substrate 14 to the cap 18. The cap 18 is made of a good heat conductive material such as copper or aluminum. The cap 18 has small cylindrical openings 22 located therein, which are arranged in 3 by 3 arrays directly adjacent to the exposed surface of each chip 12. The openings 22 contain pistons 24 opposite each of the chips 12 in the module. The pistons 24 are made of a good heat conducting material such as aluminum or copper or alloys thereof. The cap 18 is in contact with a cold plate 30 which includes a channel 32 suitable for carrying a fluid coolant such as water.
Each of the pistons 24 has a head or header 26 at the end which contacts the surface of the chip 12 when the pin-piston is inserted into the adjacent opening 22 within the housing 18. A spring 27 is included between the housing 18 and the piston 24 to give a small force of the header 26 against the surface of the chip 12. The force exerted by the spring pressure is such that it will not cause the solder balls 28 on which the chips 12 are mounted to change shape.
In operation, heat generated by the chips 12 is extracted by the headers 26 and conducted by the pistons 14 to the cap 18 and the cold plate 30. As coolant flows through the channel 32, it carries away the heat from the cold plate 30, thereby extracting the heat from the integrated circuit chips 12 within the thermal conduction module 10.
While the thermal conduction module of FIG. 1 has provided a good solution to integrated circuit cooling problems, some aspects of the module lend themselves to improvement. In particular, the structural interrelationships between the pistons and the TCM cap can be critical to module performance.
An improvement to the thermal conduction module of FIG. 1 is described in an article entitled Annulus-Convection Vertically Integrated Module Cooling, RESEARCH DISCLOSURE, MARCH 1990, Number 311 (31168). As with the module of FIG. 1, the semiconductor chips are arranged on a substrate in a row and column array. Metal pistons extending from downwardly open cylindrical holes (piston holes) in the hat are pressed against the chip to provide a conduction path for heat transfer from the chips. The pistons are spring loaded in the hat to ensure that the piston chip interface has good thermal contact.
The cooling hardware for the module is made up from a three-tier integrated hat cold plate. The lowest tier (tier-1) is the hat containing the spring loaded pistons. From the substrate side, this hat appears the same as the hat used in other conventional TCMs (such as the TCM of FIG. 1). Tier 1 has upwardly facing cylindrical holes (convection holes) located on the diagonals between the piston holes. These holes form the convective surface for cooling, and like the piston holes, do not extend through the thickness of tier-1. The top surface of tier-1 has fashioned on it distribution vanes, one between each row of holes, which directs the coolant (water) from the holes to a return manifold located at one end of tier-1.
The second tier (tier-2) has on its lower side, coolant injector nozzles which extend downward. When tier-2 is positioned on tier-1, the coolant injector nozzles are each centered in one of the convection holes of tier-1. The top surface of tier-2 has fashioned on it distribution vanes, one for each row of holes (for each injector nozzle), in manner similar to tier-1. The vanes direct the coolant from a supply manifold located at one end of tier-2 (on the opposite end of the return in tier-1) to the coolant injector nozzles. At the end of tier-2 opposite the supply manifold (and directly over the return manifold in tier-1) is located a return port which allows the coolant that collects in the return manifold to pass through, but not mix with the coolant in tier-2. Directly above tier-2 is tier-3, the cover. This tier has as its only feature the supply and return ports of conventional TCMs.
The coolant, when injected into the convection holes, first impinges against the bottom of the cylinder, providing jet impingement heat transfer. It then flows upward in the annulus created by the coolant injector nozzles and the convection surface providing additional heat transfer.
While the module of the above-described article provides an advantage over the module of FIG. 1, there remain a number of areas open for improvement. For example, the module of the above described article provides no direct means for heat to be directly conducted from the chips into the coolant injectors, this, failing to take advantage of potential surfaces to enhance convection cooling. The thermal boundary layer is larger in the above article with heat coming solely from the tier 1 convection holes. In addition, while the above described module takes advantage of jet impingement cooling, it does not match the areas of impingement cooling to the specific highly conductive paths created by tapered type pistons.